It's both embarrassing and wonderful to say that we don't know much at this point.

Titan has an atmosphere that prevents sunlight from getting down to it, so there are no shadows - so we are completely bereft of the third dimension of Titan.

All we're seeing are patterns on the surface, and we're groping, trying to understand some of these patterns.

One thing we can say about Titan's surface is it looks young - we're not seeing a surface that was created billions of years ago. It seems that it's been covered over by material; otherwise we would be seeing lots of big, circular features which would have been impact craters.

CHARLES ELACHI, JET

The US space agency's Jet Propulsion Laboratory in California is the principle US-based side of the Cassini-Huygens mission. Charles Elachi is using radar to understand Titan's topography.

Huygens rode piggyback on Cassini for seven years

Areas which are dark mean that the area is very small, and this led us to believe that most likely these are liquid areas.

The fact that they have low reflectivity is consistent with organic liquid. We don't know for sure.

Next to it, we see areas that are very bright, with triangular features. We believe these could be flows; so it could be there are fractures in the surface of Titan, and some of the material - the different hydrocarbons - is actually oozing out.

One way to think about it is that there is lots of plastic on the surface of Titan.

I wouldn't be surprised if 20 years from now, we will have craft in orbit around Titan, and have balloons in the atmosphere, surface vehicles, or landers to explore the moon in more detail.

CHRIS McKAY, AMES RESEARCH CENTER

Nasa's Ames Research Center in California supplies research and technology to support space missions.

We know that there are clouds on Titan, and that they are active - the clouds are methane, and we think that they might even be associated with rain.

The probe will hit the top of the atmosphere at six km per second

We think the surface is obscured with organic, orangey soot - like being covered with smog.

A field of organic material would be very interesting to me - I would find it quite exciting and beautiful, and be eager to study it.

One of the reasons Titan is interesting to astrobiology is that the organic reactor that's cooking on Titan right now is, in a way, possibly a model for the organic reactor that cooked on early Earth to make life.

The one difference is that on Earth, the organic reactor was in a soup of water - whereas on Titan it's a soup of liquid methane.

Somehow, just from sunlight, organic chemistry is able to build up into these complex forms┐ we've done some calculations of the energies of reactions, and we find that it's possible that if there's an organism on Titan that could survive in liquid methane the way we survived in liquid water, it could eat this organic soup being made on Titan.

They would eat it and react it with hydrogen, and there's enough energy there that they could make a go of it - if there is a methane-based lifeform, one prediction would be that there will be no settling [particles] at the surface.

JOHN ZARNEKI, OPEN UNIVERSITY

John Zarnecki is the principal investigator on Huygens's Surface Science Package, the set of instruments that will investigate conditions at ground (sea?) level.

As the probe descends, the atmosphere will flow through the "bucket" (an enclosed instrument for collecting samples) and sensors will make different measurements on that atmosphere.

Huygens will experience 900 degree Celsius heating

Then, when we land on the surface, if we should land in a liquid, the liquid will flood that enclosure and be in intimate contact with the sensors. If we land on a solid surface, or snow or ice or organic gunge, we hopefully will also get intimate contact with the sensors.

[The package] has on the end a force transducer - it will measure, in great detail, the force with which we strike the surface.

Just from that relatively simple measurement, we can tell quite a lot about the surface at the impact site.

I really would like a liquid landing - I'd like seas, or at least very large lakes, with waves on the surface.

It looks as if wind-driven waves on Titan will be very large, because of the lower gravity - one seventh Earth gravity. However, they will probably be quite slow, and very widely spaced out.

My dream scenario is to splash down... and then have the camera spy on the horizon a great big wave looming up.

The $3.2bn Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).